A Route to 2-Substituted 3-Cyanopyrroles: Synthesis of Danaidal and Suffrutine A

The title compounds were prepared in a two-step sequence from 4,4-dimethoxybutyronitrile and the respective esters by Claisen condensation and subsequent Paal-Knorr pyrrole synthesis. The sequence could be performed as a one-pot procedure delivering the pyrroles in yields of 47-72% over two steps (13 examples). Intramolecular variants of the method were applied to the total synthesis of danaidal and suffrutine A from the respective trityl-protected ω-amino alkanoates.